Method of making low inertia rotor for dynamo electric machines

ABSTRACT

The complete winding outline of a rotor, including the forward as well as the return conductor of the winding loops are applied, in flat form, to a flexible sheet, as a printed or laminated conductor. The flexible sheet has a fold line, across which the conductor portions forming the coil ends extend. The sheet is then folded along the fold line upon itself and rolled into a hollow cylinder, to form a self-supporting rotor. If desired, an internal support of a plastic, metal tube, or the like can be applied Multiple-layer windings can be formed by first applying the winding outline to the sheet, and then folding the sheet-zigzag upon itself with additional insulating layers where conductors would contact each other, and then rolling the folded sheet with the conductors thereon into a cylinder.

United States Patent [151 3,694,907 Margrain et al. [4 1 Oct. 3, 1972[54] METHOD OF MAKING LOW INERTIA 3,259,768 7/1966 Burr ..29/598 X ROTORFOR DYNAMO ELECTRIC MACHINES FOREIGN PATENTS OR APPLICATIONS 72Inventors: Pierre Mal-grain; Gerard Lacroux 955 ,291 4/1964 GreatBritain ..29/598 both of Malakoff, France Primary Examiner-Robert L.Splcer, Jr. [73] Asslgneez Etabhssements E. Ragonot Attorney nynn &Frishauf [22] Filed: July 6, 1970 211 App]. No.: 52,595 [57] ABSIRACTThe complete winding outline of a rotor, including the forward as wellas the return conductor of the winding [30] Forelgn Application PrmmyData loops are applied, in flat form, to a flexible sheet, as a July 10,1969 France ..6923496 printed or laminated conductor. The flexible sheethas a fold line, across which the conductor portions form- 310/217, ingthe coil ends extend. The sheet is then folded 310/264 along the foldline upon itself and rolled into a hollow [5 Cl. "H02k cylinder to forma e]f supporting rotor desired an [58] Field of Search.29/S98; 310/40 R,40 MM, 1 internal support of a plastic, metal tube, or the like 310/195264 can be applied Multiple-layer windings can be formed by firstapplying the winding outline to the sheet, and [56] References C'tedthen folding the sheet-zig-zag upon itself with addi- UNITED STATESPATENTS tional insulating layers where conductors would contact eachother, and then rolling the folded sheet with 3,084,420 4/1963 Burr eta1 ..29/598 the conductors thereon into a cylinder 1,738,166 12/1929Apple ..29/598 1,789,129 l/1931 Apple ..29/598 X 9 Claims, 13 DrawingFigures PATENTEDncra m2 SHEET 1 [IF 5 PATENTEDncI 3 m2 SHEET 2 [IF 5PAIENIEnncrs I972 Y s 694 907 SHEET 3 [1F 5 METHOD OF MAKING LOW INERTIAROTOR FOR DYNAMO ELECTRIC MACHINES The present invention relates torotors for dynamo electric machines, and more particularly tolow-inertia rotors utilizing printed, or laminated circuit techniques intheir manufacture.

Servo and control motors, particularly motors used in data processingequipment require rotating elements which have as low an inertia aspossible, so that they can rapidly reach a stable commanded speed fromrest, or from any other speed. Such motors are also needed to controltapes, particularly for tape transport in computer equipment which havehigh start-stop requirements with extremely low inertia.

Various types of motors with low inertia have been developed. Aparticularly useful type employs a rotor formed as a hollow cylinderwhich rotates within an air gap of a magnetic circuit which is fixed.The winding of the rotor is formed of coils having a single loop formedas printed or laminated circuits. Laminated circuits should beunderstood to mean circuits in which conductive strips are applied to aninsulating support base, for example, by adhesives, crimping or othermethods known in the art.

Rotors of the type forming a hollow cylinder are usually made by firstpreparing an outline, that is a printed (or laminated) drawing of thewindings as a printed circuit and carrying the conductors for currentflowing in one direction and then the return conductors. The two outlinedrawings, first flat, are then placed over another, rolled incylindrical form, and then interconnected at their terminal ends inorder to form the loops of the windings. This method of assemblingrequires two interconnections; one at the rear face, where the forwardand the return current carrying windings are interconnected and theother on the forward end, which may also be called the collector end.Difficulties have been experienced in making the connections,particularly in making the connections at the back end where thewindings are to be interconnected, which difficulties have been solvedonly by manually interconnecting one conductor after the other in theregion of their junctions.

It is an object of the present invention to provide a rotor, and amethod of making the rotor of low inertia, in which the windings areformed by printed or lamina circuits, and which do not require extrainterconnectrons.

SUBJECT MATTER OF THE PRESENT INVENTION:

Briefly, the outline of the conductors for an entire winding is appliedto a printed or lamina circuit support which is flexible, and has abending or a hinge line, across which the conductors extend. Thesupport, with the conductors thereon is then folded across the break orbending line, the conductor thus forming an integral loop. Thereafter,the folded support with the conductors thereon is rolled intocylindrical form, the forward current carrying and return currentconductors being separated by two thicknesses of the insulating support.The break or bend line, in form of a hinge, is bridged by the connectingportions of the winding loops at the rear (that is away from thecommutator) end of the coil, the forward end being shaped to form acollector extension. The assembly is then preferably applied to a hollowcylinder which may be plastic, resin, reinforced fiber material,cellulose material, ceramics or metal.

The hollow support cylinder is metal, and it is preferably made byelectrolytic deposition about a mandrel which is later removed; themandrel itself may consist of a central core of tough materialsurrounded by a metallic covering material having a low melting pointwhich is readily removed.

The rotor may be secured together by adhesives, or may be adhered abouta cylinder; to effect good curing of adhesives used, the rotor with itssupport cylinder is placed on a mandrel and the entire assembly insertedinto a ring-shaped pressure chamber having a rubber bladder which uponbeing charged with compressed air or other compressed fluid will tightlysurround the rotor to bond the adhesives used and the rotor into aunitary whole. The rotor may be covered with banding,

of insulating material, insulated metal sleeves or the like.

In the accompanying drawings:

FIG. 1 illustrates, a plan developed view of a complete loop of awinding for the rotor of a dynamo electric machine;

FIG. 2 is a developed plan view of the outline shape of a printed orlaminated surface, with some conductors thereon, forming one embodimentof a starting point in making the rotor in accordance with the presentinvention;

FIG. 3. illustrates an almost completed rotor in perspective view;

4 is a longitudinal, partly broken away and cross-sectional view of arotor assembled in a machine, shown in schematic form;

FIG. 5 is a top plan view of the lay-out of the windings in accordancewith a different embodiment;

FIG. 6 is a partial schematic cross-sectional view, in longitudinalsection, of the hollow metal cylinder being applied to a mandrel whichhas not yet been removed;

FIG. 7 is a schematic longitudinal view through a pressure chamberillustrating a step in the process of manufacturing a complete rotor;

FIG. 8 is a partial longitudinal cross-sectional view, in section, of anassembly of a support cylinder and winding after the process of FIG. 7has terminated;

FIG. 9 is a schematic longitudinal half cross-sectional view of a coreand mandrel in accordance with another embodiment of the presentinvention;

FIG. 10 is a partial cross-sectional longitudinal view to a greatlyenlarged scale of a rotor of FIG. 4, which is banded with a metal band;

FIG. 11 is a lay-out drawing for a multi-layer wind- FIG. 12 is apartial longitudinal cross-sectional view of one multi-layer winding,after folding of the circuit of FIG. 11; and

FIG. 13 is a partial transverse cross-sectional view of the coil of FIG.12 showing how the conductor layers, among each other areinterconnected.

The type of rotor to which the present invention relates is best seen inFIG. 4. The hollow cylinder 11 has coil windings 12 mounted thereon. Anair gap is formed between two magnets generally, schematically indicatedas N and S and a central core 13. A bearing such as balls 14 within abearing race, not shown, provides for rotation of the rotor assemblyconsisting of the cylinder 11 and windings 12, with respect to core 13.A pair of brushes 15 run on a commutator, the elements of which may beformed by straight terminal portions of the conductor forming thewinding.

The armature 12 is of the type generally known as interlaced and isformed of individual winding units, each one of one or more layers.Since the winding arrangement itself is well known, it will not bedescribed again in detail but a brief review will be given of thewinding lay-out to define the type of armature described in detail.

FIG. 1 illustrates a coil formed of a single winding. In this winding, agoing conductor A (shown in full lines) is connected to a straight inputportion E. It is connected by means of a rear bridge to a returnconductor R shown in broken lines, having a straight output terminalportion S. For purposes of further description, the input and outputportions E, S will be termed the forward portion and the interconnectingbridge the rearward portion of the winding.

A number of identical coils are arranged, all around the rotoroverlapping one above the other in such a manner that the forward, orgoing conductors all are located next to each other in the longitudinalsense of the rotor, however, in two layers, only one of which is formedby the going conductors A. The second layer is formed by the returnconductors R. The input connection of each coil which is on one of thelayers is connected to the output of an adjacent coil of the otherlayer, thus, giving a complete endless winding closed in itself, andgenerally termed an interlace wound armature.,This type of armature isselected as an example, although the invention is applicable to any kindof armatures, particularly to those in which the conductors have twolayers.

In accordance with the present invention, the outline of the armature 12is first provided on a flat sheet of printed circuit such as shown inFIG. 2. The carrier for the printed circuit is a thin, flexible sheetmaterial having a conductive surface applied to one side, for example,copper. The copper may be in sheet form printed, or laminated thereto.It is engraved in accordance with the image of the entire winding to beapplied, that is the terminal end portions E, the going conductor A, theconnecting bridge at the back of the armature, the return conductor Rand the final terminal portion S. A group of forward conductors Al A aswell as the return conductors R. R, of armature 12, when developed andin plain view, will appear as shown in F IG. 2. Taking the axis XX ofthis representation as a hinge point, and doubling over the broken lineportion, one obtains a flat sheet of two superimposed layers, which formthe conductors. It is readily seen that the array of conductors forms afamily of zig-zag, parallel tracks, the array of one side of the hingeXX having the same longitudinal dimension as the other portion, but atopposite sense of curvature, with respect to the left-right direction ofFIG. 2. Each one of these tracks will then represent a going conductorand a return conductor, respectively, of the armature and thus, form onewinding of armature 12.

In order to form a cylindrical armature, by means of the circuitassembly of FIG. 2, end portions of the insulating support 1 are cut tomatch the outlines of the first and last of the conductors Al-Rl andAn-R Thereafter, the flat sheet is folded along hinge XX so that theinsulating sheet will be at the interior of the fold. The insulatingsheets can then be adhered together, and the flat, folded form is rolledby hand or over a cylindrical mandrel into form of a cylinder in whichthe first conductors A1-R1 will be alongside that with the respectivelast conductors An-Rn. FIG. 3 illustrates, that due to the curvature inthe cylinder, several of the going conductors A will define theprojecting portion 2, whereas those of the return legs R1 will define ahollow or indented portion 3, inverse to the projecting region 2. Thelast going conductors An as well as the return conductors Rn will be,with respect to the first ones, reversely indented or projecting. Whenthe first and the last conductors are juxtaposed, the projections 2 willmatch exactly within the indentations 3 and can be placed above theother. Since the insulating face of the carrier having the originaldesign is folded interiorly, the projections2 will be placed insulation,against insulation and, upon adhering together the entire assembly intoa closed cylinder, the circuit of FIG. 2 is transformed into hollowcylinder having practically no trace at the junction. The exterior faceof the cylinder will support one of the layers of conductors, forexample, the going conductors, whereas the interior face will supportthe other layer of conductors, that is the return conductors. The twolayers are thus, naturally insulated from the other. There is nointerruption between going and return conductors of any one winding.Nevertheless, the winding terminals are free at the collector side. Aninput terminal of each winding is opposite the output terminal of anadjacent winding, in a suitable position for their interconnection. Asimple way to interconnect the terminal strips electrically consist informing a small opening 4 in the printed of lamina circuit, and thenfilling these holes with a small plug of connecting metal, such as tinwhich can be obtained by dipping the terminal ends in a solder bath, orplacing a small grain of copper through the holes providing foradhesion, for example, by compression, heating or other suitablemethods. The holes 4 may be pierced in the circuit in flat form, at thesame time when the circuit outline is engraved or otherwisemanufactured. In general it is not necessary to provide a specialconnecting element of the windings of armature assembly 12 to a separatecollector, since the straight conductive portions which form the inputand output terminals E, S, respectively, may directly serve as thetongues of the collector (see FIG. 4).

Armature 12 as described, utilizes a support for the printed circuitwhich is thin and plyable and which can be readily bent, as well asbeing rolled in cylindrical form. It may, for example, be a sheet ofpolyester, Mylar or the like of several tens of microns in thickness.The copper sheet on the support may have any desired thickness,depending on the current carrying capacity required of the armature 12and by the width of the air gap in which the armature 12 is to operate.In order to utilize the terminal ends of the windings as the collectortongues, the thickness of the terminal ends can be increased byelectrolysis at the point where the brushes will track, particularlywhen the thickness of the copper conductors forming the winding is verysmall, such as several microns only.

Embodiment of FIG. 5: The outline of the armature 12 is cut flat from asingle sheet of metal, such as copper. Conductors A1 and R1 have thesame general form as that shown in FIG. 2; they are interconnectedtogether by small metal tabs, KLM located conveniently and preferably atthe terminal end regions E, S, respectively, as well as at the level ofthe hinge X- X. The interconnection of the conductors among each otherprevents deformation and spreading apart; interconnection at threepoints permits ready handling of the cut sheet of copper. In order toform the armature by meansof a copper sheet, it is folded in half alongthe hinge X-X, and bent round over a cylindrical mandrel, or directlyover a hollow cylinder 11. After being shaped, a thin insulating tube isplaced in the interior of the fold, that is between the layers of goingconductors A and the return conductor R. Thereafter,,input and outputconductors are interconnected, and then the small tabs K, L, M are cutto sever the conductors both at the collector end, as well as at therear end of the armature.

- In accordance with a variation, the sheet of copper is cut and adheredto an insulating, flexible sheet before being bent, and then bent alonghinge axis XX and shaped as before.

Embodiment of FIGS. 11 and 12: To make a multilayer'armature 12, flatwinding outline in accordance with FIG. 11 is prepared again as aprinted circuit similar to the embodiment of FIG. 2, with interconnectedgroups of conductors as described in connection with FIG. 5. A pluralityof going and returnconductors will be provided; as seen in FIG. 11, thegoing conductors A A,,,, are connected to return conductors R R to goingconductors of the second layer A,,,. A and in turn to the returnconductors of the second layer R R,,,,. As first fold, the conductorsare then hinged about axes XX and Z-Z to form the going and returnconductors of the two layers with supporting insulating material 16therebetween, similar to the insulating material 1 of FIG. 2, or, if theconductors are made of interconnected strips of copper, for example, asheet insulating material can be interposed to separate the going andreturn conductors. Thereafter, a bend in the opposite direction isformed above hinge axis YY with an insulating sheet 17 (FIG. 12)therebetween. The array of conductors forms as group of tracks inzig-zag parallel arrangement. Each one of the conductive tracksrepresents going and return conductors of a coil having two windings.Only the going conductors of the first winding, A A and the returnconductors of the last winding R R have terminal ends which are straightin order to form the input and output portions E, S of the coils. InputE may, directly, form also the commutator segments.

The embodiment of FIG. 11 is similar to that of FIG. 2, except that ithas two windings. Similarly, insulating support film 16 is cut inaccordance with the outline of the terminal conductors A R A R and A,,,,m: nb ab The outline pattern. just cut. may then be folded atom Mm Ywith the conductors facing each other (that is the insulating sheet atthe outside), and the insulating sheet 17 is interposed and the layersof windings are then adhered together (see FIG. 12). The pattern isfolded back upon itself upon axes XX and Z-Z. The going conductors ofthe second layer A. A and the return conductors of the first layer R Rare thus separated by the insulating sheet 17. After adhesion togetherof all insulating sheets, various layers of the conductors will besuperposed as illustrated in FIG. 12. The entire assembly folded andadhered together is then rolled in the form of a cylinder, ends arecovered as best seen in FIG. 13 and fixed by adhesives.

Armatures having a larger number of winding layers than two may be madein similar fashion. The embodiment described in connection with FIG. 11and 12, shows the winding layers folded along fold hinge lines, withinsulating sheets interposed between adjacent layers of conductors.Insulating sheets may be either the support for the conductorsthemselves or may be separate sheets similar to sheet 17, inserted flatand in tubular form after the winding arrangement has rolled into acylinder.

The armature sub-assembly 12 in accordance with the invention is mountedon a hollow cylinder 11 (FIG. 4) to form the low inertia rotor assembly10.

The hollow cylinder 11, in accordance with the invention, must be verylight so that its inertia does not substantially increase that of thearmature assembly. It must be sufficiently thin to take up little spacein the air gap and, additionally, must be sufficiently rigid to retain acircular shape. Cylinder 11 may be of plastic material, cellulosicmaterial, or resin-reinforced fiber material, or of metal, if theexterior surface thereof is protected by an insulator. In case good heatremoval from the armature is desired, cylinder 11 may also be made ofberyllium oxide, a ceramic having a heat conductivity which is almostequal to that of copper. If cylinder 11 is made of metal it should,preferably, have one or several of the following characteristics: Itshould be capable of being applied by electro deposition in a thin layerhaving low internal tension, that is less than l00kg. per square cm. Forexample; it should have good mechanical strength, that is be very rigid,resistant to compressive forces, and have a high Young modulus, whilehaving a low volumetric mass; and it should have a high electricalresistivity so that the rotor, in operation, will have little eddycurrent losses.

A suitable metal is nickel. A hollow metallic cylinder 11, made ofnickel, can be made in accordance to the present invention, as follows(with reference to FIG. 6); a layer 19 is electrodeposited in a nickelsulfamate bath or a similar bath. Layer 19 will have a homogeneousthickness in the order of from 0.25 to 0.30 mm. applied on a toughcylindrical core 18, such as soft iron. Core 18 has a cylindrical body20 and a coaxial cylindrical extension 21 which functions as mechanicalaxis first for the entire core 18 during the manufacture of the hollowcylinder 11, and then may function as a shaft for the hollow cylinder11.

Core 18, with its exterior layer 19 of nickel is carefully machined forroundness. Nickel layer 19 on core 18 is covered with adhesives andinsulating resin 19 and then the armature 12, previously folded, isrolled thereon. The superimposed layers of the armature are adheredtogether. The armature itself may form as previously discussed inconnection with FIGS. 2, 5, or 1 1. After adhering the end portion ofthe winding array of armature 12, the entire sub-assembly of core-nickelcoating winding is located in a pressure chamber 22 (FIG. 7) in which aninternally hollow pressure bladder 23 is inserted. Pressure bladder 23is inflated through a duct 24 to apply itself snuggly against theoutside of the sub-assembly armature l2 layer 19 core 18, to remainthere for at least a part of the period of time of polymerization of theadhesive resin, or during another adhesion process. Heat may be suppliedif desired.

The sub-assembly: Core 18 layer 19 (with applied insulation 19) armature12 is then removed from the pressure chamber 22 and machined to removealmost, or all of the cylindrical material of core 18 (FIG 8) leaving,however, the nickel layer 19 in tact. This may be accomplished by meansof mechanical machining,

finished by chemical attack. Nickel layer 19 and the remaining portionsof core 18 (FIG. 8) will then form the hollow cylinder 11 illustrated inFIG. 4 and referred to in the preceding description.

For improved rigidity, the nickel layer 19 may be formed with a bulgedup cylindrical edge 25 (FIG. 6 and 8). The core 18 itself may already beformed with an enlarged end portion 26 (FIG. 6) to effect deposition inthe shape shown to an enlarged scale in FIG. 10.

In accordance with the present invention, the core in which the hollowcylinder will be obtained may be similar to core 27 (FIG.9) which ispartially composed of tough metal and partially a metal having a lowmelting point, in order to facilitate removal of the cylindrical bodywhich is not necessary, after the layer 19 of nickel, or another metalof suitable characteristics, has been applied on the core. Core 27 has acentral shaft 28 and disc-like end portion 29, also of tough metal, aswell as a cylindrical body of low-melting point metal, or alloy; amelting temperature of from 100 C. to 130 C. is suitable.

After the roundness of the core 27 is accurately established, it isfirst covered with a thin layer of copper, for example, byelectrodeposition, and then covered with a layer 19 of another metalsuch as nickel. Nickel layer 19 has the armature 12 applied thereto asdescribed previously. The sub-assembly: Nickelcoveredcore 27, andinsulation; and armature 12 is then if desired, inserted in the pressurechamber (FIG.7); to remove the metal, it is subjected to a temperaturejust above the melting point of the metal, or the metal alloy formingthe cylindrical body 30. The metal forming body 30 is carved out,leaving intact the layer 19 of nickel with an internal thin film ofcopper. Any residual low-melting point metal is removed by machining.The copper base film forming the plating substrate may either remain, ormay be removed chemically.

Rotors 10 which are to operate at high speed preferably are banded onthe outside. In accordance with the invention, and exterior insulatinglayer 31 covers the conductor of armature 12, which for mechanicalstrength may be metalized in accordance with electrodepositiontechniques, for example, by a thin layer 32 of a metal such as nickel(see FIG.10). In order to make the hollow cylinder 11 as light apossible, relief holes 33 (FIG. 8 and FIG. 9) may be pierced through theend faces, so that it will function similar to a spider.

As had been seen, the motor is easily manufactured from a flat, plainsheet. The lay-out of the conductive 6 strips to form the windings maybe carried out by well known printed circuits or laminated circuittechniques on a flat surface, whichare then folded as desired. Contraryto the priorart, which requires separate manufacture of going and returnconductors, and interconnection of the windings both at the commutatorend as well as at the rear end of the armature, the present inventionprovides a rotor structure and a method of making such a rotor in whichthe number of parts to be handled and to be made is decreased, thus,substantially facilitating alignment and interconnection of the separateparts. The only interconnection to be made is the collector side. Inaccordance with the invention, the two terminal conductors of thearmature assembly, when rolled in a cylinder, match exactly withoutnecessity of providing interconnection of the conductors of thewindings, one each, thus omitting additional connection points andsimplifying manufacture and assembly.

The present invention has been described specifically in connection withsingle and multi-layer windings armatures having interlaced windings;oth'er winding systems, and different winding arrangement may be usedwithin the scope of the inventive concept.

We claim: 1. Method of manufacturing low inertia rotors for dynamoelectric machines comprising providing an array of unitary, integralconductor lines in plan outline and having a central fold line (X-X),said conductor lines being arranged in plan outline of complete windingloops and having a first slating portion to form the end of the winding,a straight portion essentially transversed to said fold line to form afirst active portion of the winding loop; second and third slantingportions, extending up to, through, and beyond said fold linerespectively; a second straight portion essentially transverse to saidfold line to form a return active portion of the winding loops; and afourth slanting portion forming the other end of the winding;

applying at least said first and second slanting portions and said firststraight portion to a sheet of insulating material;

folding said conductor lines about said fold lines so that saidconductor portions will lie opposite each other separated by said sheetof insulating material;

rolling said folded conductor lines with said insulating sheet intocylindrical form;

securing terminal ends of said sheet with said conductor lines thereontogether to retain cylindrical form;

electrodepositing a layer of metal (19) on a cylindrical support (18,27) to form a cylindrical metal layer;

placing said folded cylindrically-formed sheet with said conductor linesthereon on said electrodeposited cylindrical metal layer; and

removing at least a major portion of said cylindrical support whileleaving said cylindrical metal layer to form a hollow, low inertia,composite cylindrical rotor structure.

2. Method according to claim 1, wherein said support comprises a toughmetal including soft iron.

3. Method according to claim 1, wherein said support comprises acomposite of a central cylindrical body of tough metal and a cylindricalcovering of a metal of low melting point.

4. Method according to claim 3 comprising the further step of firstdepositing a cover layer on the cylindrical body of low melting pointmetal before electrodepositing said layer of metal (19).

5. Method according to claim 1 including the step of 5 applying aninsulating layer (31) to the exposed surface of said conducting line atthe outside of said cylindrically formed sheet;

and banding (FIG. -32) the outside of said cylindrically formed sheet.

6. Method according to claim 5, wherein the step of handing comprisesthe step of electro-depositing a metallic layer on the outside of saidinsulating layer (31) covering the exposed conductive lines.

7. Method of manufacturing low inertia rotors for dynamo electricmachines comprising providing an array of unitary, integral conductorlines in plan outline and having a central fold line (X-X), saidconductor lines being arranged in plan outline of complete winding loopsand having a first slanting portionto form the end of the winding, astraight portion essentially transversed to said fold line to form afirst active portion of the winding loop; second and third slantingportions, extending up to, through, and beyond said fold linerespectively; a second straight portion essentially transverse to saidfold line to form a return active portion of the winding loops; and afourth slanting portion forming the other end of the winding; applyingat least said first and second slanting portions and said first straightportion to a sheet of insulating material;

folding said conductor lines about said fold lines so that saidconductor portions will lie opposite each other separated by said sheetof insulating material;

rolling said folded conductor lines with said insulating sheet intocylindrical form; securing terminal ends of said sheet with saidconductor lines thereon together to retain cylindrical form by insertingsaid rolled, cylindrical sheet about a mandrel (19, 18, 27);

inserting said mandrel with said rolled sheet and conductive linesthereon into a pressure chamber having a resilient ring-shaped pressurebladder (23) of flexible material;

and applying a pressure fluid inside said bladder to apply uniformpressure to the outside of said cylindrically rolled sheet and againstsaid mandrel.

8. Method according to claim 7, including the step of applying aninsulating layer (31) to the exposed surface of said conducting line atthe outside of said cylindrically formed sheet;

and banding (FIG. 10-32) the outside of said cylindrically formed sheet.

9. Method according to claim 8, wherein the step of banding comprisesthe step of electro-depositing a metallic layer on the outside of saidinsulating layer (31) covering the exposed conductive lines.

1. Method of manufacturing low inertia rotors for dynamo electricmachines comprising providing an array of unitary, integral conductorlines in plan outline and having a central fold line (X-X), saidconductor lines being arranged in plan outline of complete winding loopsand having a first slating portion to form the end of the winding, astraight portion essentially transversed to said fold line to form afirst active portion of the winding loop; second and third slantingportions, extending up to, through, and beyond said fold linerespectively; a second straight portion essentially transverse to saidfold line to form a return active portion of the winding loops; and afourth slanting portion forming the other end of the winding; applyingat least said first and second slanting portions and said first straightportion to a sheet of insulating material; folding said conductor linesabout said fold lines so that said conductor portions will lie oppositeeach other separated by said sheet of insulating material; rolling saidfolded conductor lines with said insulating sheet into cylindrical form;securing terminal ends of said sheet with said conductor lines thereontogether to retain cylindrical form; electrodepositing a layer of metal(19) on a cylindrical support (18, 27) to form a cylindrical metallayer; placing said folded cylindrically-formed sheet with saidconductor lines thereon on said electrodeposited cylindrical metallayer; and removing at least a major portion of said cylindrical supportwhile leaving said cylindrical metal layer to form a hollow, lowinertia, composite cylindrical rotor structure.
 2. Method according toclaim 1, wherein said support comprises a tough metal including softiron.
 3. Method according to claim 1, wherein said support comprises acomposite of a central cylindrical body of tough metal and a cylindricalcovering of a metal of low melting point.
 4. Method according to claim 3comprising the further step of first depositing a cover layer on thecylindrical body of low melting point metal before electrodepositingsaid layer of metal (19).
 5. Method according to claim 1 including thestep of applying an insulating layer (31) to the exposed surface of saidconducting line at the outside of said cylindrically formed sheet; andbanding (FIG. 10-32) the outside of said cylindrically formed sheet. 6.Method according to claim 5, wherein the step of banding comprises thestep of electro-depositing a metallic layer on the outside of saidinsulating layer (31) covering the exposed conductive lines.
 7. Methodof manufacturing low inertia rotors for dynamo electric machinescomprising providing an array of unitary, integral conductor lines inplan outline and having a central fold line (X-X), said conductor linesbeing arranged in plan outline of complete winding loops and having afirst slanting portion to form the end of the winding, a straightportion essentially transversed to said fold line to form a first activeportion of the winding loop; second and third slanting portions,extending up to, through, and beyond said fold line respectively; asecond straight portion essentially transverse to said fold line to forma return active portion of the winding loops; and a fourth slantingportion forming the other end of the winding; applying at least saidfirst and second slanting portions and said first straight portion to asheet of insulating material; folding said conductor lines about saidfold lines so that said conductor portions will lie opposite each otherseparated by said sheet of insulating material; rolling said foldedconductor lines with said insulating sheet into cylindrical form;securing terminal ends of said sheet with said conductor lines thereontogether to retain cylindrical form by inserting said rolled,cylindrical sheet about a mandrel (19, 18, 27); inserting said mandrelwith said rolled sheet and conductive lines thereon into a pressurechamber having a resilient ring-shaped pressure bladder (23) of flexiblematerial; and applying a pressure fluid inside said bladder to applyuniform pressure to the outside of said cylindrically rolled sheet andagainst said mandrel.
 8. Method according to claim 7, including the stepof applying an insulating layer (31) to the exposed surface of saidconducting line at the outside of said cylindrically formed sheet; andbanding (FIG. 10-32) the outside of said cylindrically formed sheet. 9.Method according to claim 8, wherein the step of banding comprises thestep of electro-depositing a metallic layer on the outside of saidinsulating layer (31) covering the exposed conductive lines.